Colorectal cancer is a major cause of cancer deaths in men and women in developed countries, and over a million new cases and 500,000 deaths occur each year. Inherited susceptibility to colorectal cancer only accounts for 15-25% of all cases, whereas, 75-85% of colon cancer is sporadic and associated with environmental/dietary factors. Studies in this laboratory have identified a series of 1,1-bis (3'-indolyl)-l- (p-substituted phenyl) methanes [C-substituted diindolylmethanes (DIMs)], which exhibit low in vivo toxicity but inhibit colon tumor and colon cancer cell growth through activation of peroxisome proliferator-activated receptor y (PPARy). We hypothesize that PPARy-active C-substituted DIMs represent a new class of mechanism-based drugs for treatment of colon cancer. Aim 1 will further investigate activation of PPAR ? -dependent transactivation and coactivator recruitment using a series of analogs containing both p-phenyl and indole ring substituents. These and other studies will be carried out in six colon cancer cell lines with defined molecular features including at least two cell lines which express wild-type PPARy (HT-29) and K422Q mutant PPARy, (HCT-15), which are non-responsive to other PPARy agonists such as rosiglitazone. The comparative growth inhibitory activities of rosiglitazone and PPARy-active C-substituted DIMs in colon cancer cell lines will be extensively investigated. Aim 2 will focus on the mechanisms of growth inhibition by PPARy-active C-substituted DIMs and based on preliminary studies, which appear to be associated with cell cycle genes/proteins (p21 and cyclin D1) and markers of differentiation such as caveolin 1 and 2. Initial studies will focus on the role of caveolin induction by PPARy-active C-substituted DIMs as a critical pathway for inhibition of cancer cell growth using wild-type and PPAR? -inactivated cells through RNA interference. Aim 3 will investigate inhibition of colon tumor growth in transgenic Min mice that are susceptible to colon cancer and athymic nude mouse models bearing colon cancer cells as xenografts and treated with PPARy-active C-substituted DIMs. The proposed studies will provide mechanistic insights on PPARy-dependent inhibition of colon cancer and identify compounds for future clinical studies.